A “Runner’s High” refers to the feeling of euphoria that follows a workout. Experts often attribute this feeling to the release of endorphins, but new research claims it’s more like smoking a joint. A study published in the Proceedings of the National Academy of Sciences has found that a runner’s high is achieved via the brain’s endocannabinoid system, which is the same one that is affected by the tetrahydrocannabinol (THC) in marijuana.

“A runner’s high is a subjective sense of well-being some humans experience after prolonged exercise,” the German research team wrote. “For decades, it was hypothesized that exercise-induced endorphin release is solely responsible for a runner’s high, but recent evidence has suggested that endocannabinoids also may play a role.”

Researchers monitored two groups of mice, one that ran on a treadmill for five hours and one that remained sedentary. Anxiety levels for each group were gauged using the dark-light box test — the mouse’s anxiety is measured by the frequency and speed it took them to leave a well-lit area for a darker area that offers a place to hide. They also tested each animal’s tolerance for pain by placing them on a hot plate to see if they would jump or lick their paws.

The mice in the treadmill group were considered less anxious following their five-hour run compared to mice in the sedentary group. Not only were mice considered less anxious, but they also had a higher tolerance for pain. However, mice that ran on a treadmill for five hours were still considered anxious and sensitive to pain when researchers dosed both groups of mice with a chemical that blocked endocannabinoids, suggesting the process does have something to so with feelings of euphoria.

“Here, we demonstrate that wheel running increases endocannabinoids and reduces both anxiety and sensation of pain in mice,” researchers added. “Ablation of cannabinoid receptor 1 receptors on GABAergic neurons inhibits running-induced anxiolysis, and pharmacological blockage of central and peripheral cannabinoid receptors inhibits analgesia. We thus show for the first time to our knowledge that cannabinoid receptors are crucial for main aspects of a runner’s high.”

No matter what the cause of a runner’s high, it does seem they are beneficial toward an athlete’s overall health. A recent study led by researchers from the University of Iowa showed that some of the cardiac benefits tied to exercise come from the subsequent release of opioid peptides. It could also improve on the efficiency of a runner’s workout by benefiting their V02 Max — top oxygen uptake — and strength.

Source: Fuss J, Steinle J, Bindila L, Auer M, Kirchherr H, Lutz B, Gass P. A runner’s high depends on cannabinoid receptors in mice. Proceedings of the National Academy of Sciences. 2015.